1. Field of the invention
The present invention relates to the structure of a fiber network, and more particularly to a detection system for identifying faults in a passive optical network.
2. Description of the Prior Art
In the prior art, when one of the fiber branches of a fiber communication network has a fault, it is very important to discover the broken fiber branch and the broken position of the fiber branch as fast as possible. Thereby, the fiber communication network can maintain the quality of signal transmission.
The detection system of the prior art is shown in FIG. 1. The detection system includes a main control section 1, a fiber trunk connected to the main control section, a plurality of fiber branches connected to the fiber trunk via a splitter 2, and a plurality of user stages respectively connected to a corresponding fiber branch.
The main control section 1 includes a plurality of signal sources, an optical circulator 15, a first coupling unit that includes a wavelength division multiplexing (WDM) coupler 18, and an optical coupler, a pumping source 16, and a hookup survival detection unit 17. The hookup survival detection unit 17 can be an optical spectrum analyzer (OSA). Each of the fiber branches is a single mode fiber and includes a fiber Bragg grating (FBG) such as an FBG 31, 41, 51, or 61, a thin film filter such as the thin film filter 33, 43, 53, or 63, and a user stage such as the user stage 35, 45, 55, or 65.
The first signal source 11 provides a data signal λ1. The second signal source 12 provides a data signal λ2. The third signal source 13 provides a data signal λ3. The fourth signal source 14 provides a data signal λ4. The coupler couples the data signals to the optical circulator 15, and the optical circulator 15 transmits the data signals to the WDM coupler 18 for being further fed into the fiber trunk. Next, the splitter 2 transmits the data signals from the fiber trunk to each of the fiber branches, wherein each fiber trunk has the data signals λ1 through λ4 transmitted within.
Otherwise, the pumping source 16 simultaneously provides a pumping laser light λ5 to the fiber trunk that includes a single mode fiber SMF and an Erbium-doped fiber EDF. The pumping laser light λ5 pumps the Erbium-doped fiber EDF to emit an amplified spontaneous emission (ASE) with a band as detection signals such as the detection signals λ51 through λ54.
Because each of the FBGs has its individual center wavelength (Bragg condition), the center wavelength of each FBG is set to equal the frequency of each detection signal. Because each of the thin film filters has its individual transmission frequency band, the transmission frequency band of each thin film filter is set to equal the frequency band of each data signal.
Hence, each of the data signals is transmitted to the corresponding user stage, and each of the detection signals is reflected to generate a corresponding reflected signal. The data signal λ1 is transmitted to the first user stage 35, and the detection signal λ51 is reflected to generate the reflected signal λ′51. The data signal λ2 is transmitted to the second user stage 45, and the detection signal λ52 is reflected to generate the reflected signal λ′52. The data signal λ3 is transmitted to the third user stage 55, and the detection signal λ53 is reflected to generate the reflected signal λ′53. The data signal λ4 is transmitted to the fourth user stage 65, and the detection signal λ54 is reflected to generate the reflected signal λ′54.
Finally, the reflected signals are transmitted back to the hookup survival detection unit 17. The hookup survival detection unit 17 further uses the reflecting signals to identify whether each fiber branch has a fault or not. The spectrum of the signal transmitted in the broken fiber branch is different to the spectrum of the signal transmitted in an unbroken fiber branch.
However, the detection system of the prior art cannot discover the fail position of the broken fiber branch. This disadvantage causes difficultly to the user stages performing maintenance work on the fiber communication network.